This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We propose to study a variety of proteins using synchrotron radiation. These include immunologically important molecules such as catalytic antibodies, anti-HIV antibodies, MHC/TCR complexes, NKG2D-receptor complexes, IL-2/receptor complexes, CD1, and CD3. We will also study the purine biosynthesis enzymes GAR transformylase and ATIC in complex with inhibitors. Finally, we will use the MAD technique to determine the structures for p115, a cell trafficking molecule and for CD14, the main lipopolysaccharide sensor on macrophages.